Crystallographically textured tantalum oxide (Ta2O5) demonstrates approximately twice the dielectric permittivity of amorphous Ta2O5, making c-axis textured Ta2O5 very attractive as a DRAM cell dielectric. Metallic ruthenium is the bottom cell plate of choice for crystallographically textured, high permittivity Ta2O5 cell dielectrics because the Ta2O5 orders on the hexagonal close-packed (hcp) ruthenium structure and provides the high permittivity texturing.
Historically, there have been adhesion issues when ruthenium is deposited on silicon dioxide (SiO2) and other dielectric films. This adhesion issue on oxide dielectrics has been addressed by adding disilane (Si2H6) to the initial stages of ruthenium deposition. However, X-ray photoelectron spectrometry (XPS) analysis and secondary ion mass spectrography (SIMS) show that about 20 atomic percent silicon is present at the top surface of the deposited ruthenium film, which adversely affects the desired crystographically textured Ta2O5 deposition.
It would be desirable to provide a process for fabricating a ruthenium film that overcomes these problems.